Ballast circuit

ABSTRACT

A ballast circuit for operating at least one gaseous discharge lamp from a high voltage input utilizing a transformer having two secondary windings, which may be used with either a high or low voltage input. The transformer also includes a primary winding, one side of which is connected to the junction of the first and second secondary windings. The other side of the primary winding is connected to ground, as is the fixture in which the at least one lamp is mounted. This provides a lamp power circuit loop including the two secondary windings and a lamp starting-aid circuit including the primary and only one of the secondary windings.

United States Patent 1191 [111 3,898,517 Starling Aug. 5, 1975 BALLAST CIRCUIT Primary livaminer-James W. Lawrence [75] lnvemor' James A. a Dam/1H6 [1" Assistant EmminerE. R. LaRoche [73] Assignee: General Electric Company,

Indianapolis, Ind. [57 ABSTRACT [22] Filed: June 14, 1974 A ballast circuit for operating at least one gaseous discharge lamp from a high voltage input utilizing a [211 App! 479888 transformer having two secondary windings, which may be used with either a high or low voltage input. [52] U.S. Cl. 315/278; 315/257; 315/276; The n f r lso n ludes a primary winding, one 315/])[(} 5 side of which is connected to the junction of the first [51] Int, Cl, 1105B 41/232; H0513 41/234 and second secondary windings. The other side of the [58] Field of Search 315/257, 262, 274, 276, p m ry in ing is onnected to ground, as is the fix- 315/278 DIG 5 ture in which the at least one lamp is mounted. This provides a lamp power circuit loop including the two [56] Refe Cit d secondary windings and a lamp starting-aid circuit in- UNITED STATES PATENTS cluding the primary and only one of the secondary windings. 3,160,784 l2/l964 Strecker 315/278 3,792,310 2/1974 Crawford 315/257 4 Claims, 1 Drawing Figure BALLAST CIRCUIT BACKGROUND OF THE INVENTION This invention relates to a ballast circuit for operating at least one gaseous discharge lamp. More particularly, it relates to a ballast circuit which utilizes a transformer operating on a relatively high input voltage, and may use secondary windings which are normally used with relatively low input voltages.

Gaseous discharge lamps, such as fluorescentlamps. have a negative resistance characteristic. That is, as the current through the lamp increases, the resistance de creases thereby allowing more and more current to be drawn by the lamp. If the current is allowed to continue to increase the lamp electrodes will become overheated and the lamp will be destroyed. It is therefore necessary to limit the current through a gaseous discharge lamp by providing a ballast for it. Ballasts utilizing transformers and capacitors have been found to efficiently limit the current. These transformers and capacitors have been placed in series with the lamp so as to reactively ballast the lamp.

The basic line voltage utilized by homes, offices, and many other buildings is 120 v rms, 277 v rms is used in factories and other such locations. Therefore, ballasts utilizing 120 v rms input are produced in relatively high volume, while ballasts utilizing 277v rms input are produced in relatively low volume. Even though 277v input ballasts are now relatively low volume items, they are becoming more and more significant. Therefore, it would be efficient to utilize common parts for both the 120v and 277v ballasts. Since the 120v ballast is a high volume ballast, it is desirable to try to make the 277v ballast using the 120v ballast components as much as possible.

One item which has been looked at extensively is the use of the 120v system secondary windings in 277v ballasts. The primary winding, which receives the input voltage, was provided with an increased number of turns for the 277v system. However, the secondary windings were kept with the same number of turns, therefore, the same secondary windings were used for both ballasts.

The specifications for a typical 8-foot 1,500 milliampere fluorescent lamp require the ballast to provide 650 volts peak from one lamp electrode to ground, which is normally a nearby fixture, for assuring starting of the lamp. Such ballasting systems also must operate under certain other constraints. For instance, lampholders commonly used with lamps ofthis type have a.

600 volt rms rating.

A ballast can be constructed using a typical 120v ballast secondary winding and a primary winding have the increased number of turns required for a 277v input operation. If the high voltage side of the primary winding is connected to the low voltage side of the secondary winding, the full voltages of both the primary and the secondary windings appear between one lamp end, and thus the associated lampholder, and ground. This will cause the rms voltage at one of the lampholders to exceed the 600 v rms rating of normally used lampholders. If the neutral, or grounded, side of the primary winding is connected to the low voltage side of the secondary winding, the primary winding voltage does not; appear in the lamp starting-aid circuit and the ballast will not deliver the 650v peak from one lamp electrode to ground required to start the lamp.

OBJECTS or THE INVENTION Accordingly, it is one object of this invention to provide an improved ballast circuit for operating at least one gaseous discharge lamp from arelatively high voltage input.

Another object is to provide a ballast circuit having a transformer for receiving a high input voltage but utilizing secondary windings suitable for high production, low input voltage applications.

Another object is to provide a ballast circuit for providing sufficient starting and operating voltage for at least one gaseous discharge lamp which remains within the appropriate ratings for the various components of the lighting system.

SUMMARY OF THE INVENTION In accordance with one form of the present invention there is provided a ballast circuit for operating at least one discharge lamp. The circuit comprises a transformer having a primary winding and first and second secondary windings. The secondary windings are serially interconnected and one end of the primary winding is connected to the junction between the secondary windings. The circuit includes means for connecting theprimary winding to a source of A.C. electric energy. The circuit also includes means for connecting the distal ends of the secondary windings to at least one gaseous discharge lamp mounted in a grounded fixturefor providing a lamp power circuit loop includingthe secondary windings. There is means for connecting the other end of the primary winding to ground for providing a lamp. starting-aid circuit including the primary winding and only one of the secondary windings.

BRIEF DESCRIPTION OF THE DRAWINGS The subject matter which is regarded as the invention v is set forth in the appended claims. The invention itself, however, together with other objects and advantages thereof may be better understood by reference to the following description taken in conjunction with the accompanying drawing in which:

The FIGURE is a schematic diagram of a ballast circuit employing one form of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now more particularly to the drawing there is provided a ballast circuit utilizing a transformer 3 having a primary winding 4 and a secondary winding arrangement 5. In the exemplification embodiment, the secondary winding arrangement 5 is split into separate secondary windings 6 and 7. However, secondary winding arrangement 5 may be a single winding having a tap therein. The primary and secondary windings are mounted on core 8. Primary winding 4 is connected across input terminals 1 and 2 to receive an input from a source of A.C. electric energy. Primary winding 4 is wound to receive a relatively high voltage, which in the exemplification embodiments is 277v rms. The secondary windings 6 and 7 are adapted to be used either vwith a high or low voltage input. For example they may be used interchangeably with a 277v rms input primary, as in the exemplification, or with a v rms input primary.

This interchangeability provides for manufacturing efficiency. In fact the primary winding for the 277 v rms ballast is designed so that a 120v rms input secondary winding design can be used in the 277v rms ballast with little or no change in the secondary winding {arrangement. Some 120v rms secondary winding arrangements are designed with two separate coils which are placed on opposite sides of the primary winding on the transformer core. Such secondary winding'designs offer the opportunity for the most economical use in 277v rms ballasts, as they can be used without modification. However, other secondary winding designs can be successfully used. For instance a continuous winding design could be used. With such a design an intermediate tap would have to be provided in the secondary for the 277v rms applications. The 277v rms secondary could then be considered to have two secondary windings, i.e. the turns on each side of the intermediate tap could be considered a separate secondary winding.

One end or side 9 of primary winding 4 is connected to the junction of secondary windings 6 and 7 through lead 11. When the ballast is installed in a lamp fixture or other operating situation, the other end or side 22 of the primary winding is connected to ground as indicated by the grounding symbol,

A capacitor 14 is connected to the distal end or side 12 of secondary winding 6 and to lamp electrode 16. The distal end or side 13 of secondary winding 7 is connected to the other lamp electrode 17. Heating windings l8 and 19 are connected respectively to electrodes 16 and 17 and are magnetically coupled to primary winding 4 for preheating the electrodes of the lamp, for minimizing the necessary starting voltage.

Lamp is mounted in close physical relationship with fixture 20 which is connected to ground at 21. The lamp l5 normally is mounted to the fixture by means of lampholders, which are well known in the art.- They have not been illustrated for the sake of simplicity. The lampholders have a twofold purpose. First, they: provide for physical mounting of the lamp in the fixture,

with the lamp electrically insulated from the fixture.

Secondly, they provide electrical connections between the lamp and its operating circuit.

Some fluorescent lamps require rather high startingaid voltages to ignite. For instance it is common for 8- foot, 1,500 milliampere fluorescent lamp specifications to require a starting-aid voltage of 650v peak to assure ignition. The starting aid voltage is a voltage between the high voltage electrode and an adjacent grounded metal surface, usually part of the lamp fixture. On the other hand, lampholders normally used with such fluo-- rescent lamps have a rrns voltage rating of 600 volts.

That is, more than 600v rrns should not appear between the lampholder contacts and ground.

Such dual requirements make it difficult to design commercially acceptable ballasts particularly for operation with high voltage supplies. By the present invention, applicant has provided a new and improved ballast circuit. The present invention meets the required design criteria and, at the same time, allows the use of certain relatively high production volume 120v compo-. nents in low production volume 277v ballasts.

A ballast circuit as shown in the drawing has beenbuilt and successfully operated an eightfoot fluorescent lamp, using components having the following set.

of values:

Core 8 center leg area of 1.4 square inches. Primary Winding 792 turns of aluminum wire having a 0.0320 inch bare conductor diameter Secondary Windings 6 & 7 770 turns each of aluminum wire having a 0.0430 inch bare conductor diameter 7 Heating Windings l8 and 19 12 turns each of copper wire having a 0.0226 inch bare conductor diameter.

Capacitor l4 7,9 mfd Lamp 15 General Electric Catalog No. F96PG17 exempl ification embodiment the voltage on primary winding 4 is 352v peak and the voltage on secondary winding 6 is approximately 320v peak when the input voltage is of rated input. The sum of these two peak .voltages is sufficient to meet the peak voltage specification for starting an 8-foot, 1,500 milliampere fluorescent lamp. A return path for the starting-aid circuit is provided from ground 21 of the fixture 20 to grounded side 22 of primary winding 4'through the utility system.

Once the lamp begins to conduct a lamp power circuit loop is formed and includes secondary winding 6 and 7, capacitor 14 (which is part of the ballasting means and provides power factor correction) and lamp 15. The primary winding voltage is not included in the lamp power circuit loop. During lamp operation approximately 200 volts rms appears across each of the secondary windings 6 and 7. Thus the voltage between either of electrodes l6, l7 and ground 21 will be less than 600 volts rms, the rms voltage rating of normally i is intended in the appended claims to cover all modifications that fall within the true scope and spirit of this invention.

What 1 claim as new and desire to be secured by Letters Patent of the United States is:

l. A ballast circuit for operating at least one gaseous discharge lamp, comprising:

a transformer having a primary winding and first and second secondary windings; said first and second secondary windings being serially interconnected and one end of said primary l winding being connected to the junction between said first and second secondary windings; means for connecting the distal ends of said first and second secondary windings to at least one gaseous discharge'lamp mounted in a grounded fixture for providing a lamp power circuit loop including only said first and second secondary windings of said transformer windings; and

first and second secondary windings are formed as two separate coils, with a length of conductor therebetween.

4. A ballast circuit as set forth in claim 1 wherein said first and second secondary windings are formed from a single. essentially continuous coil having an intermediate tap. 

1. A ballast circuit for operating at least one gaseous discharge lamp, comprising: a transformer having a primary winding and first and second secondary windings; said first and second secondary windings being serially interconnected and one end of said primary winding being connected to the junction between said first and second secondary windings; means for connecting the distal ends of said first and second secondary windings to at least one gaseous discharge lamp mounted in a grounded fixture for providing a lamp power circuit loop including only said first and second secondary windings of said transformer windings; and means for connecting the other end of said primary winding to ground for providing a lamp starting-aid circuit including only said primary winding and one of said secondary windings of said transformer windings.
 2. A ballast circuit as set forth in claim 1; further including a capacitor connected to one of said secondary windings and the lamp.
 3. A ballast circuit as set forth in claim 1 wherein said first and second secondary windings are formed as two separate coils, with a length of conductor therebetween.
 4. A ballast circuit as set forth in claim 1 wherein said first and second secondary windings are formed from a single, essentially continuous coil having an intermediate tap. 